Effects of Organic and Inorganic Amendments on Fractionation of Cadmium during Incubation Time in a Contaminated Calcareous Soil

The addition of heavy metals to the soil leads to change of their original distribution pattern. Distribution of heavy metals in soil depends on the type of metal, application level, time and soil characteristics as well. In order to study the effect of organic amendments (bichar 640 and 420) and inorganic amendments (zeolite, bentonite, leca and pumice) on chemical forms of Cd during incubation time in a calcareous soil, a factorial experiment was conducted in a completely randomized design (CRD) with 3 levels of amendments application in soil (0, 1 and 5 %) in three replications. Chemical distribution of Cd in soil was determined using Tessier sequential extraction method during 90- and 180-days incubation time. Results showed that during incubation time, Cd concentration increased in exchangeable (6.05%), carbonated (13.25) and decreased the oxide fraction (7.41%), organic fraction (10.74%) and residual fractions (2.98%) during the time. The application of bentonite (5%) were the most effective treatment in decreasing Cd concentration in exchangeable fraction during the incubation time that this decrease was 1.89%. Application of the organic amendments (biochar 640 and biochar 420) and inorganic amendments (pumice, leca bentonite, and zeolite) decreased the exchangeable fraction of Cd compared to the control. Application of 5% (w/w) of biochar 640 showed the highest decreasing the exchangeable fraction of Cd that compared to the control, it showed a decrease of 41.79%. The organic and inorganic amendments were effective on the immobilization of Cd in soil. However, the organic amendments were more efficient in immobilization of Cd than the inorganic amendments. These results might due to the high amount of organic carbon and cation exchange capacity of the organic amendments than the inorganic amendments.